(1) Field of the Invention
The present invention relates to the field of equipment for rotary wing aircraft, in particular for helicopters, and it relates to feeding energy to members that are fitted to the rotorcraft. Said members are more particularly power members such as at least one power plant for driving a rotor in rotation, and accessories and/or pieces of equipment that are useful for the working of the rotorcraft.
The present invention relates more specifically to architectures for supplying a rotor fitted to a helicopter or an analogous rotary wing aircraft with mechanical power derived from hybrid energy sources, and for managing this power supply by means of an on-board electrical network of the rotorcraft.
(2) Description of Related Art
The concept of hybrid energy sources should be considered with respect to selectively using a combustion energy source and/or an electrical energy source. The combustion energy source makes use in particular of a turboshaft engine or an internal combustion engine of the diesel engine type, and the electrical energy source makes use in particular of a reversible electric machine, and more particularly a generator/starter.
The concepts of a turboshaft engine, of an internal combustion engine, of a reversible electric machine, and of a generator/starter should not be considered narrowly, but broadly with respect to their operating mode and the ways they are implemented. More particularly, a turboshaft engine, an internal combustion engine, and a reversible electric machine, in particular a generator/starter, may be replaced by members that are commonly accepted as being analogous in terms of their operating mode and the ways they are implemented.
Helicopters are rotary wing aircraft having at least one rotor driven in rotation by at least one power plant. In the context of the present invention, consideration should be given more particularly to a hybrid power plant associating a combustion engine and an electric motor, in particular a reversible electric machine.
The rotor may be a main rotor providing the rotorcraft with its lift, and also its propulsion in a helicopter. The rotor may also be a secondary rotor such as a tail rotor serving to guide the rotorcraft about a yaw axis, or indeed a propulsive propeller in the context of a long-range high-speed rotorcraft, traditionally referred to as a hybrid helicopter.
The rotor is commonly driven in rotation by a power plant comprising at least one engine driving a main gearbox that mechanically engages the rotor. In a variety of variants associated essentially with the power of the rotorcraft and with regulations concerning the kind of territory over which the rotorcraft is allowed to fly, a rotorcraft may have a single engine or it may have more than one engine, and in particular it may be a two-engined rotorcraft. Conventionally, a single-engined rotorcraft has a turboshaft engine or an internal combustion engine, in particular a diesel engine, while a two-engined rotorcraft has two turboshaft engines. Each turboshaft engine associates a gas generator engaging a free turbine for driving rotation of the main gearbox.
The main gearbox may also be used for mechanically driving major pieces of equipment of the rotorcraft that require significant amounts of power in working, such as for example a pump or a compressor of a ventilation, heating, and/or air conditioning device. Such major pieces of equipment include a secondary power member that is mechanically driven by the main gearbox.
Furthermore, a rotorcraft is fitted with an on-board electrical network for electrically powering various pieces of equipment and/or accessories of the rotorcraft. In order to operate, those accessories require powering at a level that is considered as being moderate relative to the mechanical power that needs to be delivered for driving the rotor, and more particularly for driving the main gearbox. Such moderate power accessories of a rotorcraft are conventionally electrically powered in working from the on-board electrical network.
By way of example, the accessories may be control panel accessories and/or comfort accessories, on-board instrumentation providing information about the working and/or the environment of the rotorcraft, or indeed calculation accessories controlling the operating mode of the rotorcraft. It should be observed that these accessories include members for making the operating mode of the rotorcraft safe and/or members for providing people with safety, or indeed members that are found to be essential for enabling the pilot to guide the rotorcraft in complete safety via a man-machine interface (MMI).
The on-board network is in communication with various sources of electrical energy, such as a reversible electric machine, an electricity generator, and/or an electrical energy store. The on-board network has one or more central units controlling the distribution of energy flows to the various accessories and pieces of equipment of the rotorcraft that are to be supplied with electrical energy, or indeed to power members such as a said reversible electric machine that is capable of being used for temporarily driving the engine.
It is appropriate to ensure that the working of a rotorcraft is safe given the available electrical energy. For example, according to document FR 2 961 767 (Sagem Defense Sécurité), proposals are made to interrupt recharging electrical energy into an energy store for electrically powering an accessory of a rotorcraft in the event that an engine of the rotorcraft is in operation and said energy store is at a predefined charge threshold.
For this purpose, central units have connection interfaces (buses) in communication with various switch members, such as contactors or analogous switch members. The electrical energy resources of the rotorcraft are managed by the central units that control the flows of electrical energy passing via the on-board network.
Depending on needs, the central units control the supply of electrical power to the on-board electrical network and the distribution of this electrical power to an electricity distribution network form which auxiliary electrical networks are powered for electrically powering accessories and pieces of equipment of the rotorcraft.
The on-board electrical network is a sensitive installation of the rotorcraft and it is important to ensure that it is constantly fed with electrical energy and that it constantly has power available. It is necessary to be able to obtain a suitable electrical power supply for the various pieces of equipment and accessories of the rotorcraft regardless of the flight situations and/or the stages of flight of the rotorcraft.
Flight situations correspond in particular to a situation of starting or stopping a rotor, a situation of hovering flight, and/or a situation of low-speed flight, corresponding to the rotorcraft advancing at less than 40 knots (kt), or indeed to a situation of cruising flight in which the power plant of the aircraft is used at a nominal speed. Stages of flight correspond to a change in engine speed, such as a stage of starting or stopping the power plant, and in particular to transient stages during which the power plant is accelerated or decelerated.
Traditionally, a machine that generates electricity is incorporated in the power plant for the purpose of being driven in rotation by the engine. The electric machine delivers electricity to the on-board network and is used to feed an electrical energy store that makes it possible, where necessary, to power the on-board network.
Under such conditions, changes in technology and in requirements have led to organizing the architecture for delivering mechanical power to the rotor from a plurality of energy sources associating an engine with a reversible electric machine. Such architectures are commonly referred to as hybrid power plant architectures.
In addition to the mechanical energy contribution delivered to the rotor by the engine, the reversible electric machine is used as a drive member capable of temporarily delivering extra mechanical energy in specific flight situations and/or flight stages of the rotorcraft. By way of example, the reversible electric machine is used when starting the rotorcraft in order to initiate drive of the engine. Also by way of example, it is possible to make use of a configuration in which the reversible electric machine is engaged with the drivetrain used for driving the rotor to provide the engine with assistance during an acceleration stage, or conversely during a deceleration stage.
For example, according to document US 2009/0145998 (Ival O. Salyer), a turboshaft engine delivers the mechanical energy normally required by the rotor in a cruising flight situation. An electric motor is used for driving the rotor in predetermined flight conditions. The electric motor may be electrically powered by the on-board network from an electrical energy store, or from an electricity generator that is mechanically driven by a turboshaft engine.
Also by way of example, according to document U.S. Pat. No. 7,513,120 (United Tech. Corp.), electric machines are mechanically engaged on a turboshaft engine, one via the gas generator and the other via the free turbine. The efficiency and the performance of the gas generator are improved during transient flight stages in the operation of the engine.
Reference may also be made to document FR 2 929 324 (Turbomeca SA), in which a reversible electric machine is selectively mechanically engaged with the gas generator in order to start the engine, or with the free turbine in order to be driven in an electricity generator mode.
Document FR 2 914 697 (Turbomeca SA) proposes a hybrid power plant architecture for a rotorcraft in which electrical energy is used during transient flight stages, in particular during an acceleration or a deceleration stage.
Under such circumstances, an auxiliary electric motor is engaged with the gas generator of a turboshaft engine driving the rotor in order to assist it in an acceleration stage. The auxiliary motor is electrically powered from an electrical energy store or from a first electricity generator. The first electricity generator may be driven by the free turbine of the engine or by the mechanical drivetrain used for driving the rotor.
A second electricity generator is engaged with the gas generator in order to take mechanical energy therefrom during a deceleration stage and transform the mechanical energy it takes into electrical energy. The second electricity generator feeds electrical energy to an electrical energy store when it is driven by the gas generator. Still with respect to deceleration, the auxiliary motor may be a reversible electric machine operated to take mechanical energy from the gas generator.
A problem raised lies in reconciling delivering top-up mechanical energy from a reversible electric machine in order to drive the rotor, with safe working of the on-board network faced with the electricity needs of the rotorcraft. Account should also be taken of the possibility whereby a hybrid power plant architecture can be installed without major structural modification on board any type of rotorcraft, in particular a single-engined rotorcraft or a two-engined rotorcraft.
This difficulty is addressed in document FR 2 962 404 (Eurocopter), which discloses a hybrid power plant architecture fitted to a rotorcraft. A solution proposed in that document is in particular to draw a distinction between the on-board network operating under a nominal electric voltage and an auxiliary electrical network that is specifically reserved to the reversible electric machine operating at its own auxiliary electric voltage.
It is appropriate to optimize the use of the electric machine for delivering mechanical drive to the rotor. This seeks in particular to use a reversible electric machine to the best of its capacities, regardless of the flight situations and/or the transient flight stages of the rotorcraft.
More precisely, the reversible electric machine must be capable of being used regardless of the flight situation of the rotorcraft as considered from the stage of starting the rotor to a cruising flight situation, and vice versa, while including critical flight situations of the rotorcraft progressing at low speeds and/or hovering.
In particular, the reversible electric machine must be used during transient flight stages in which the engine needs to be assisted mechanically by the reversible electric machine in order to drive the rotor when accelerating.
More particularly in an acceleration stage, it is appropriate to deliver the top-up mechanical energy from the reversible electric machine in order to drive the rotor. Still more particularly, in a deceleration stage, it is appropriate to use the reversible electric machine and/or an electricity generator to take mechanical energy from the drivetrain for driving the rotor in rotation.
Such advantages provided by the hybrid power plant architecture need to be obtained without affecting the working of the on-board network of the rotorcraft. It is therefore also appropriate to guarantee the reliability and safe working of the on-board network. The electrical energy resources of the on-board network need to be kept available and sufficient regardless of the immediate needs of the rotorcraft, and without affecting the safety of its operation.
A quantity of electrical energy must be kept available for safe working of the various pieces of equipment and accessories in the rotorcraft. The availability of this quantity of electrical energy must not be obtained to the detriment of attempts at simplifying the hybrid power plant architecture and must take account of the electrical energy needs of numerous pieces of equipment and accessories that might be fitted to the rotorcraft. For a given mission profile of the rotorcraft, it is also important to avoid wasting energy.
Account must also be taken of it being desirable for the hybrid power plant architecture to be installed on any type of rotorcraft without requiring major structural modification, and in particular regardless of the number of engines with which the rotorcraft might be fitted and regardless of the structure of the engine used for driving the rotor, i.e. whether it is an internal combustion engine or a turboshaft engine, in particular.
Consequently, it appears not to be easy to design an architecture for delivering mechanical power to a rotorcraft rotor from hybrid energy sources while complying with all of the above-mentioned constraints.